Process for the production of aromatic carbamates

ABSTRACT

A process for producing aromatic carbamates in high yield is described, which comprises reacting aromatic nitro compounds, organic compounds containing a hydroxy group, and carbon monoxide in the presence of a catalyst comprising: (1) a platinum group metal or its compound, (2) metallic vanadium or its compound, (3) metallic iron or its compound, (4) a halogen atom, and (5) a tertiary amine, wherein the amount of each component used and the composition are adjusted within specific ranges.

FIELD OF THE INVENTION

The present invention relates to a process for the production ofaromatic carbamates. More particularly, it is concerned with a processfor the production of aromatic carbamates which comprises reacting anaromatic nitro compound, an organic compounds containing a hydroxy groupand carbon monoxide in the presence of a catalyst.

BACKGROUND OF THE INVENTION

Aromatic isocyanates are used as starting materials for the preparationof polyurethane and, commercially, they are usually prepared by reactingaromatic amines obtained by hydrogen-reduction of aromatic nitrocompounds with phosgene. This method, however, is rather complicatedand, furthermore, has disadvantages in that it utilizes phosgene whichis a toxic gas, and hydrogen chloride is generated at the phosgenationreaction, causing the problem of corrosion of equipment.

In recent years, therefore, several methods of production of aromaticisocyanates not using phosgene have been proposed. For example, there isknown a method in which aromatic nitro compounds are reacted withcompounds containing a hydroxy group and carbon monoxide in a liquidphase in the presence of a catalyst to prepare the correspondingaromatic carbamates and, thereafter, the carbamates are thermallydecomposed to obtain aromatic isocyanates. This method requires acatalyst exhibiting high catalytic activity in a small amount in thepreparation of aromatic carbamates. Conventional catalysts which haveheretofore been proposed include a catalyst comprising (1) a platinumgroup metal, e.g., palladium, (2) a Lewis acid, e.g., ferrous chloride,and (3) a tertiary amine, e.g., pyridine (see Japanese PatentApplication (OPI) No. 98240/76(the term "OPI" is used herein to mean a"published unexamined Japanese patent application")), and a catalystcomprising (1) palladium, (2) vanadium oxychloride, and (3) a tertiaryamine (see Japanese Patent Application (OPI) No. 22339/79). Althoughthese catalysts have fairly high catalytic activity, there has beenproposed a further improved catalyst comprising (1) a platinum groupmetal, (2) a Lewis acid, e.g., ferrous chloride, and (3) an oxide or anacid salt of a metal, e.g., vanadium (see Japanese Patent Application(OPI) No. 128550/79).

These conventional catalysts, however, are not considered to havesufficient catalytic activity for practical use and, furthermore, sinceconsiderably large amounts of iron and/or vanadium compounds are used,they suffer from disadvantages in that the amount of the metal or metalsbeing incorporated into the desired product crystals is increased whenthe crystals are separated by crystallization after the completion ofthe reaction.

As a result of extensive investigations to overcome the above-describedproblems and to provide a catalyst which exhibits a high catalyticactivity even in a small amount, it has been found that a catalystcomprising a platinum group metal, vanadium, iron, a halogen atom, and atertiary amine wherein the amounts of vanadium and iron used are reducedand the amount of the halogen atom to the total atom of the metals iscontrolled within a specific range prevents corrosion of equipment,inhibits the formation of by-products, particularly those which cannotbe converted into the desired product, and produces the desired aromaticcarbamate in high yield.

DISCLOSURE OF THE INVENTION

The present invention, therefore, relates to a process for producing anaromatic carbamate by reacting an aromatic nitro compound, an organiccompound containing a hydroxy group and carbon monoxide in the presenceof a catalyst, which is characterized in that the catalyst comprises (1)from 0.5 to 20 mmol of a platinum group metal or its compound (in thiscase, calculated as the metal), (2) from 1 to 70 mmol of metallicvanadium or its compound (in this case, calculated as the vanadiummetal), (3) from 0.3 to 50 mmol of metallic iron or its compound (inthis case, calculated as the iron metal), (4) from 30 to 400 mmol of ahalogen atom, and (5) a tertiary amine, all being based on one kilogramof the organic compound containing a hydroxy group to be fed to thereaction system, and the molar ratio of the halogen atom to all themetals being from 0.5/1 to 60/1.

The invention will hereinafter be explained in detail.

Aromatic nitro compounds which can be used in the invention includemononitrobenzenes, such as nitrobenzene, nitrotoluene, nitroxylene,chloronitrobenzene, bromonitrobenzene, nitrophenyl carbamate,nitroanisol, nitrobenzaldehyde, nitrobenzoyl chloride,ethyl-p-nitrobenzoate, nitrobenzenesulfonyl chloride, and nitrophthalicanhydride; dinitrobenzenes, such as dinitrobenzene, 2,4- or2,6-dinitrotoluene, 1-chloro-2,4-dinitrobenzene, and1-fluoro-2,4-dinitrobenzene; and trinitrobenzenes, such as2,4,6-trinitrotoluene. In addition, nitronaphthalenes, nitrobiphenyls,bis(nitrophenyl)alkanes, bis(nitrophenyl)ethers,bis(nitrophenyl)thioethers, bis(nitrophenyl)sulfonic acids,bis(nitrophenoxy)alkanes, heteroaromatic nitro compounds, etc., can beused. These compounds can be used alone or in combination with eachother.

Organic compounds containing a hydroxy group which can be used in theinvention include monohydric alcohols, such as methanol, ethanol,propanol, butanol, amyl alcohol, hexanol, lauryl alcohol, cetyl alcohol,cyclohexyl alcohol, benzyl alcohol, and chlorobenzyl alcohol; polyhydricalcohols, such as ethylene glycol, diethylene glycol, propylene glycol,glycerine, and hexanetriol; monohydric phenols, such as phenol,propylphenol, butylphenol, β-naphthol, anthrol, and phenanthrol; andpolyhydric phenols, such as catechol, resorcine, pyrogallol, anddihydroxydiphenylmethane. These alcohols or phenols may be substitutedby a substituent or substituents which are inert to the reaction, suchas a halogen atom, a sulfonic acid group, and a carboxylate group. Theabove-described compounds can be used alone or in combination with eachother.

In the reaction between the aromatic nitro compound and the organiccompound containing a hydroxy group, it is theoretically required to usethese compounds in such amounts that the molar ratio of the hydroxygroup of the organic compound containing a hydroxy group to the nitrogroup of the organic nitro compound is 1/1. In the invention, however,it is usually preferred that a solvent is not used, but that the organiccompound containing a hydroxy group is added in such an amount that themolar ratio of the hydroxy group to the nitro group exceeds 1/1, so thatthe organic compound containing a hydroxy group also acts as a solvent.For example, the organic compound containing a hydroxy group is used insuch an amount that the molar ratio of the hydroxy group to the nitrogroup is from 2/1 to 400/1 and preferably from 5/1 to 50/1.

The catalyst of the invention essentially comprises (1) a platinum groupmetal or its compound, (2) metallic vanadium or its compound, (3)metallic iron or its compound, (4) a halogen atom, and (5) a tertiaryamine.

Examples of the above catalyst component (1) (i.e., platinum group metalcomponent) include palladium, rhodium, ruthenium, platinum, iridium, andosmium, and their compounds, such as halides, e.g., chlorides andbromides; cyanides; thiocyanides; oxides; inorganic acid salts, e.g.,sulfates, nitrates and carbonates; and organic acid salts, e.g.,oxalates and acetates. Of these metals and their compounds, palladiumand its compounds, particularly halides and oxides are preferred. Morepreferred are metallic palladium, palladium chloride, and palladiumoxide. The platinum group metal component may be deposited on a support,such as activated carbon, graphite, and diatomaceous earth, in an amountof from 0.2 to 5% by weight. The amount of the platinum group metalcomponent (being used) is from 0.5 to 20 mmol, preferably from 0.8 to 15mmol, as calculated as a metal per one kilogram of the organic compoundcontaining a hydroxy group to be fed to the reaction system. When theamount of the platinum group metal component added is too small, nosufficient catalytic activity can be obtained.

Examples of the catalyst component (2) (i.e., vanadium component)include vanadium and its compounds, such as halides, e.g., vanadiumtrichloride, vanadium tetrachloride, vanadium oxydichloride, vanadiumoxytrichloride, vanadium pentachloride, vanadium tribromide, vanadiumtetrabromide, vanadium oxytribromide, vanadium triodide, vanadiumpentaiodide, vanadium oxydiiodide, and vanadium oxytriiodide; oxides,e.g., vanadium trioxide and vanadium pentoxide; vanadic acids and theirsalts, e.g., pyrovanadic acid, metavanadic acid, sodium orthovanadate,potassium metavanadate, and ammonium metavanadate; sulfates, e.g.,vanadium sulfate and vanadyl sulfate; oxalates, e.g., vanadium oxalateand vanadyl oxalate; carbonates, e.g., vanadium carbonate and vanadylcarbonate; vanadium acetylacetonate; vanadium oxyacetylacetonate; VO(OC₂H₅)₃ ; and V(CO)₆. Of these compounds, the halides, oxides, oxalates,and carbonates of vanadium, vanadium acetylacetonate, and VO(OC₂ H₅)₃are preferred. The amount of the vanadium component used is from 1 to 70mmol, preferably from 2 to 60 mmol, as calculated as a metal per onekilogram of the hydroxy-containing organic compound. When the amount ofthe vanadium component is outside the above-specified range, nosatisfactory results can be obtained. The vanadium component is added insuch an amount that the molar ratio of the metal in the vanadiumcomponent to the metal in the platinum group metal component is from 0.1to 15 and preferably from 0.5 to 12.

As the catalyst component (3) (i.e., iron component), metallic iron andiron compounds, such as iron halides, e.g., ferrous chloride, ferricchloride, ferrous bromide, ferric bromide, and ferrous iodide; ironoxides, e.g., ferrous oxide and ferric oxide; iron hydroxides; ironsulfates, e.g., ferrous sulfate and ferric sulfate; iron carbonates,e.g., ferrous carbonate and ferric carbonate; iron oxalates, e.g.,ferrous oxalate and ferric oxalate; iron acetylacetonate, and ironphthalocyanine can be used. Of these compounds, metallic iron, and thehalides, oxides, hydroxides, carbonates and oxalates of iron arepreferred. The amount of the iron component (used) is from 0.3 to 50mmol, preferably from 0.5 to 30 mmol, as calculated as a metal per onekilogram of the hydroxy group-containing organic compound. Usually themolar ratio of the metallic iron in the iron component to the metal inthe platinum group metal component is within the range of from 0.02/1 to12/1 and preferably from 0.1/1 to 10/1. When the amount of the ironcomponent is outside the above-specified range, sufficiently highcatalytic activity cannot be obtained. The molar ratio of the metalliciron in the iron component to the metal in the vanadium component isusually from 0.01/1 to 20/1 and preferably from 0.05/1 to 10/1. As inthe case of the platinum group metal component, the vanadium componentand the iron component may be deposited on a support. In this case, thecomponents may be deposited on the same support or different supports.

The halogen atom of the catalyst component (4) is used in the form ofhydrogen halide, such as hydrogen chloride, hydrogen bromide, orhydrogen iodide. A preferred halogen atom is chlorine, which ispreferably used as hydrogen chloride. Although the hydrogen halide canbe supplied directly to the reaction system, it is preferred to supplyas a tertiary amine-hydrogen halide salt as described hereinafter. Inaddition, the halogen atom can be used in the form of halides ofplatinum group metal, vanadium or iron as described hereinbefore. Thesemetal halides may be used in combination with the above tertiaryamine-hydrogen halide salt. The amount of the halogen atom used is from30 to 400 mmol, preferably from 40 to 300 mmol, per one kilogram of theorganic compound containing a hydroxy group, and the molar ratio of thehalogen atom to all the metals is 0.5/1 to 60/1 and preferably from0.8/1 to 40/1. When the amount of the halogen atom used is too small, nosufficient catalytic acitvity can be obtained, whereas when it is tolarge, undesirable side-reactions occur.

Tertiary amines which can be used as the catalyst component (5) of thepresent invention include aliphatic amines, e.g., triethylamine,tripropylamine, and tributylamine; aromatic amines, e.g.,N,N-dimethylaniline, N,N-diethylaniline, and triphenylamine; alicyclicamines, e.g., N,N-dimethylcyclohexylamine, N,N-diethylcyclohexylamine,and N,N-dipropylcyclohexylamine; heterocyclic amines such as pyridine,pyridine derivatives, e.g., chloropyridine, bromopyridine,fluoropyridine, 2,6-dichloropyridine, 4-phenylpyridine, picoline,2-methyl-5-ethylpyridine, 2,6-lutidine, collidine, 2-vinylpyridine,2-chloro-4-methylpyridine, 4-phenylthiopyridine, 2-methoxypyridine,2,6-dicyanopyridine, phenyl α-picolinate, methyl α-picolinate, andα-picolinic acidamide, quinoline, quinoline derivatives, e.g.,isoquinoline, chloroquinoline, and 5,6,7,8-tetrahydroquinone, pyrrolederivatives, imidazole derivatives, indole derivatives, and carbazolederivatives. Of these compounds, pyridine, quinoline, isoquinoline, andtheir derivatives are preferred. The amount of the tertiary amine (used)is from 10 to 5,000 mmol, preferably from 100 to 3,000 mmol, per onekilogram of the hydroxy group-containing organic compound. Usually themolar ratio of the tertiary amine to the halogen atom is from 0.01/1 to20/1, preferably from 1/1 to 10/1. When the amount of the tertiary amine(used) is too large, the rate of reaction is reduced, whereas when it isto small, the corrosion of reaction equipment is undesirablyaccelerated. Where a hydrogen halide salt is used as a tertiary amine,it acts as both the tertiary amine component and the hydrogen halidecomponent.

The reaction of the invention can be carried out either batchwise orcontinuously. In the batchwise method, an aromatic nitro compound, anorganic compound containing a hydroxy group, and a catalyst are chargedinto a reaction system, temperature of the reaction system is raisedand, thereafter, the pressure in the reaction system is increased byintroducing thereinto carbon monoxide and the reaction is carried outunder stirring. The reaction temperature is usually from 100° to 250°C., preferably from 140° to 200° C., and the reaction pressure isusually from 1 to 200 kg/cm², preferably from 30 to 100 kg/cm². Thereaction time is usually from 10 minutes to 15 hours, preferably from 1to 10 hours.

After the reaction is completed, the reaction mixture is passed througha filter to separate the platinum group metal component, etc., which arepresent in a solid form and, thereafter, the mother liquor is cooled toprecipitate aromatic carbamate crystals which are then recovered byfiltration. Since the mother liquid usually contains the catalystcomponents other than the platinum group metal component, it ispreferably recycled to the reaction system and reused.

The catalyst of the invention exhibits greatly high catalytic activityeven when it is used in a small amount. In particular, the amounts ofthe vanadium component and the iron component used are small and,therefore, when the deisred product is crystallized out after thecompletion of the reaction, the amount of metals contained in thecrystals formed is reduced and furthermore the loss of the catalyst isdecreased.

Best Mode of the Invention

The following examples are given to illustrate the invention in greaterdetail although the invention is not limited thereto. The concentrationsof the catalyst components mean the amounts of each metal in themetallic component of the catalyst, halogen atom, and tertiary amine perone kilogram of the organic compound containing a hydroxy group.

EXAMPLE 1

A 1.5-liter autoclave made of titanium was charged with 38.25 g of2,4-dinitrotoluene (hereinafter referred to as "DNT") and 300 ml ofethanol which had been dehydrated by the use of molecular sieves and,furthermore, with 5.0 g of metallic palladium deposited on activatedcarbon in an amount of palladium metal of 2% by weight (Pdconcentration: 3.95 mmol/kg), 369 mg of VCl₃ (V concentration: 9.9mmol/kg), 228 g of FeCl₃ (Fe concentration: 5.93 mmol/kg), 2.5 g of apyridine hydrochloric acid salt (Cl concentration: 139 mmol/kg;including Cl in the metallic compound), and 6.09 g of pyridine. Afterthe atmosphere in the autoclave was replaced by N₂ gas, the temperaturewas raised to 140° C. and CO gas was introduced under pressure to 80kg/cm² G and, thereafter, the temperature was raised to 160° C. Thereaction was carried out under stirring for 4 hours.

After the reaction was completed, the autoclave was allowed to cool andto return to the atmospheric pressure. The reaction mixture wasfiltered, and the filtrate was analyzed by high-speed liquidchromatography to determine the yields of the desired product,diethyltolylene-2,4-dicarbamate (hereinafter referred to as"diurethane"), an intermediate product, ethyl-methylnitro carbanilate(hereinafter referred to as "nitrourethane"), and a by-product,ethyl-methylamino carbanilate (hereinafter referred to as"aminourethane"). The results are shown in Table 1.

COMPARATIVE EXAMPLES 1-4

The procedure of Example 1 was repeated wherein the catalyst componentof vanadium or iron compound was not used. The results are shown inTable 1.

                  TABLE 1                                                         ______________________________________                                               Composition and Concen-                                                       tration of Catalyst                                                           Component                                                                               Cl/All                                                                              Yield                                                           V        Fe       Metals                                                                              Di-    Nitro-                                         (mmol/   (mmol/   (molar                                                                              urethane                                                                             urethane                              No.      kg)      kg)      ratio)                                                                              (%)    (%)                                   ______________________________________                                        Example 1                                                                              9.90     5.93     7.01  96      0                                    Comparative                                                                            --       5.93     11.0  14     76                                    Example 1                                                                     Comparative                                                                            --       15.8     7.01  23     66                                    Example 2                                                                     Comparative                                                                            9.90     --       8.73  34     57                                    Example 3                                                                     Comparative                                                                            15.8     --       7.01  53     40                                    Example 4                                                                     ______________________________________                                    

COMPARATIVE EXAMPLES 5-11

The procedure of Example 1 was repeated wherein the concentration ofeach catalyst component was varied. The concentration of each catalystcomponent, the ratio of Cl/all metals, and the results are shown inTable 2. The Cl concentration includes the Cl in the metallic compounds.

                                      TABLE 2                                     __________________________________________________________________________           Composition and Concentration of Catalyst Component                                                   Cl/All                                                                            Yield (%)                                                                 Metals    Nitro-                                                                             Amino-                          Comparative                                                                          Pd    V     Fe    Cl    (molar                                                                            Diurethane                                                                          urethane                                                                           urethane                        Example                                                                              (mmol/kg)                                                                           (mmol/kg)                                                                           (mmol/kg)                                                                           (mmol/kg)                                                                           ratio)                                                                            (%)   (%)  (%)                             __________________________________________________________________________    5      0.40  9.90  5.93  139   8.6  5    78   0                               6      3.95  0.50  5.93  139   13.0                                                                              38    53   0                               7      3.95  80.0  5.93  139   1.5 80     6   3                               8      3.95  9.90  0.15  139   9.9 69    24   1                               9      3.95  9.90  60.0  139   1.9 78     8   2                               10     3.95  9.90  5.95   20   1.0  3    77   0                               11     3.95  9.90  5.95  500   25.0                                                                              79     1   8                               __________________________________________________________________________

EXAMPLES 2-6

The procedure of Example 1 was repeated under the reaction conditionsshown in Table 3 and using the catalyst components shown in Table 4. Theresults are shown in Table 5.

                  TABLE 3                                                         ______________________________________                                        Exam-                  Reaction Reaction                                                                              Reaction                              ple   DNT     Ethanol  Temperature                                                                            Pressure                                                                              Time                                  No.   (g)     (ml)     (°C.)                                                                           (kg/cm.sup.2 G)                                                                       (hr)                                  ______________________________________                                        2     78.0    300      160      90      4                                     3      38.25  300      160      80      4                                     4     40.0    300      170      80      5                                     5      38.25  300      165      90      4                                     6     80.0    300      160      80      4                                     ______________________________________                                    

                                      TABLE 4                                     __________________________________________________________________________                                                    Halogen                       Platinum Group                                                                              Vanadium (Va)                                                                             Iron (Fe)             Atom/All                      Metal Component                                                                             Component   Component  Halogen Atom                                                                             Atoms Tertiary Amine                   Concen-     Concen-    Concen-    Concen-                                                                            (molar                                                                              Com-                                                                              Concen-             Ex.                                                                              Compound                                                                            tration                                                                            Compound                                                                             tration                                                                            Compound                                                                            tration                                                                            Compound                                                                            tration                                                                            ratio)                                                                              pound                                                                             tration             __________________________________________________________________________    2  2% Pd/C                                                                             6.33 VO(acac).sub.2                                                                       19.8 Fe(acac).sub.2                                                                      8.9  iQ.HCl                                                                              250  7.13  iQ  750                 3  2% Pd/C                                                                             2.77 VO(OC.sub.2 H.sub.5).sub.3                                                           11.1 FeCl.sub.2 -Py.sub.2                                                                11.1 Py.HCl                                                                              190  7.6   Py  308                 4  RhCl.sub.3                                                                          5.23 VOCl.sub.3                                                                            3.92                                                                              Fe    0.786                                                                              Q.HCl 253  25.5  Q   506                 5  2% Pd/C                                                                             3.16 V.sub.2 O.sub.5                                                                      11.9 FeCl.sub.3                                                                          5.93 Py.HCl                                                                              127  6.0   Py  127                 6  2% Pd/C                                                                             7.91 VCl.sub.3                                                                            19.8 FeCl.sub.3                                                                          11.9 Py.HCl                                                                              277  7.0   Py  831                 __________________________________________________________________________     Note 1                                                                        Concentration: mmol/kg                                                        Pd/C: Palladium deposited on activated carbon                                 Py: Pyridine                                                                  Q: Quinoline                                                                  iQ: Isoquinoline                                                              acac: CH.sub.3 COCHCOCH.sub. 3                                                Note 2                                                                        The concentration of halogen atom is a value including the halogen            contained in the metallic compound. Also the concentration of tertiary        amine is a value including the tertiary amine contained in the tertiary       aminehydrogen halide salt, and in the metallic compound.                 

                  TABLE 5                                                         ______________________________________                                        Example       Yield (%)                                                       No.           Diurethane                                                                              Nitrourethane                                         ______________________________________                                        2             87        1                                                     3             91        0                                                     4             90        0                                                     5             92        0                                                     6             93        0                                                     ______________________________________                                    

EXAMPLES 7-8 AND COMPARATIVE EXAMPLES 12-13

The procedure of Example 1 was repeated using the catalyst componentsshown in Table 6 and the reaction was carried out for 3 hours. Theresults are shown in Table 7.

                                      TABLE 6                                     __________________________________________________________________________                                                    Halogen                       Platinum Group Vanadium (V)                                                                             Iron (Fe)             Atom/All                      Metal Component                                                                              Component  Component  Halogen Atom                                                                             Metals                                                                              Tertiary Amine                    Concen-    Concen-    Concen-    Concen-                                                                            (molar                                                                              Com-                                                                              Concen-             Compound  tration                                                                            Compound                                                                            tration                                                                            Compound                                                                            tration                                                                            Compound                                                                            tration                                                                            ratio)                                                                              pound                                                                             tration             __________________________________________________________________________    Ex. 7                                                                             2% Pd/C                                                                             3.95 V.sub.2 O.sub.5                                                                     31.6 FeCl.sub.2 -Py.sub.2                                                                15.8 Py.HCl                                                                              300  5.8   --  300                 Ex. 8                                                                             2% Pd/C                                                                             0.901                                                                              V.sub.2 O.sub.5                                                                     50   Fe    20   Q.HBr 300  4.23  --  300                 Comp.                                                                             PdCl.sub.2                                                                          0.901                                                                              V.sub.2 O.sub.5                                                                     471  FeCl.sub.2 -Py.sub.2                                                                242   --   486  0.68  --  484                 Ex. 12                                                                        Comp.                                                                             2% Pd/C                                                                             4.77 VOCl.sub.3                                                                          83.9 FeCl.sub.3                                                                          83.9  --     503.4                                                                            2.92  Py  257                 Ex. 13                                                                        __________________________________________________________________________     Note                                                                          The symbols for the compounds and the concentraton of catalyst component      are the same as described in Notes 1 and 2 of Table 4.                   

                  TABLE 7                                                         ______________________________________                                                Yield (%)                                                                     Diurethane                                                                             Nitrourethane                                                                             Aminourethane                                    ______________________________________                                        Example 7 92         0           3                                            Example 8 89         2           4                                            Comparative                                                                             79         5           5                                            Example 12                                                                    Comparative                                                                             72         3           7                                            Example 13                                                                    ______________________________________                                    

EXAMPLE 9

A feed consisting of 61.50 g of nitrobenzene and 250 ml of ethanol wasreacted at 170° C. and 90 kg/cm² G and 5 hours in the presence of acatalyst comprising 2.50 g of activated carbon with 5% of metallicpalladium deposited thereon (Pd concentration: 5.93 mmol/kg), 203 mg ofVO(COO)₂, H₂ O (V concentration: 5.93 mmol/kg), 2.00 g of activatedcarbon with 4% (as metallic iron) of Fe₂ O₃ deposited thereon (Feconcentration: 7.12 mmol/kg), 2.4 g of a pyridine-hydrogen bromide saltand 1.19 g of pyridine (halogen atom concentration: 75.9 mmol/kg; molarratio of halogen atom to all metals: 4.0/1). The yield of urethane was94%.

INDUSTRIAL APPLICABILITY

Aromatic carbamates prepared by the method of the invention can beconverted into the corresponding aromatic isocyanates. Thus the methodof the invention is particularly useful in the production of aromaticisocyanates.

We claim:
 1. A process for producing an aromatic carbamate by reactingto a temperature of from 100° to 250° C., at a pressure of from 1 to 100Kg/cm² and at a time of from 10 minutes to 15 hours an aromatic nitrocompound, a monohydric alcohol or a monohydric phenol, and carbonmonoxide in the presence of a catalyst wherein the catalystcomprises:(1) from 0.5 to 20 mmol of a platinum group metal or a halide,cyanide, thiocyanide, oxide, nitrate, carbonate, sulfate, oxalate oracetate thereof (calculated as a metal); (2) from 1 to 70 mmol ofmetallic vanadium or its compound (calculated as vanadium metal); (3)from 0.3 to 50 mmol of metallic iron or its compound (calculated as ironmetal); (4) from 30 to 40 mmol of a halogen atom; and (5) from 10 to5,000 mmol of a heterocyclic amine, all of the above (1) thru (5) beingcalculated per one kilogram of the monohydric alcohol or monohydricphenol fed to the reaction system, and the molar ratio of halogen atomto all metals is from 0.5/1 to 60/1.
 2. The process as claimed in claim1, wherein the platinum group metal or its compound is metallicpalladium or a halide, cyanide, thiocyanide, oxide, nitrate, carbonate,sulfate, oxalate or acetate thereof.
 3. The process as claimed in claim2, wherein the palladium compound is a halide, oxide, nitrate, carbonatesulfate, oxalate or acetate of palladium.
 4. The process as claimed inclaim 1, wherein the vanadium compound is a halide, oxide, oxalate orcarbonate of vanadium, vanadium acetylacetonate, or VO(OC₂ H₅)₃.
 5. Theprocess as claimed in claim 1, wherein the iron compound is a halide,oxide, hydroxide, sulfate, carbonate or oxalate of iron, ironacetylacetonate, or iron phthalocyanine.
 6. The process as claimed inclaim 1, wherein the halogen atom is chlorine or bromine.
 7. The processas claimed in claim 6, wherein the halogen atom is used as hydrogenhalide.
 8. The process as claimed in claim 1, wherein the heterocyclicamine is pyridine, quinoline, isoquinoline or a derivative thereof. 9.The process as claimed in any of claims 1 to 7 and 8, wherein thearomatic nitro compound is a mononitrobenzene or a dinitrobenzene. 10.The process as claimed in claim 9, wherein the mononitrobenzene isnitrobenzene or nitrotoluene,and the dinitrobenzene is dinitrobenzene ordinitrotoluene.
 11. The process as claimed in claim 1, wherein themonohydric alcohol is methanol or ethanol, and the monohydric phenol isphenol.
 12. The process as claimed in claim 1, wherein the molar ratioof the hydroxy group in the monohydric alcohol or monohydric phenol tothe nitro group in the aromatic nitro compound is from 2/1 to 400/1. 13.The process as claimed in claim 1 wherein the catalyst comprises:(1)from 0.8 to 15 mmol of the platinum group metal or halide, cyanide,thiocyanide, oxide, nitrate, carbonate, sulfate, oxalate or acetatethereof (calculated as a metal); (2) from 2 to 60 mmol of metallicvanadium or its compound (calculated as vanadium metal); (3) from 0.5 to30 mmol of metallic iron or its compound (calculated as iron metal); (4)from 40 to 300 mmol of the halogen atom; and (5) from 100 to 3,000 mmolof the tertiary heterocyclic amine, all of the above (1) thru (5) beingcalculated per one kilogram of the monohydric alcohol or monohydricphenol, and the molar ratio of halogen atom to all metals being from0.8/1 to 40/1.
 14. The process as claimed in claim 1, wherein the molarratios of the catalyst components are as follows:(i) vanadium/platinumgroup metal=0.1/1 to 15/1; (ii) iron/platinum group metal=0.02/1 to12/1; (iii) iron/vanadium=0.01/1 to 20/1; and (iv) tertiary heterocyclicamine/halogen atom=0.01/1 to 20/1.